A variety of fluid delivery systems have been utilized in the medical field for delivering fluids (e.g., medication, nutrition, saline, etc) to a patient at relatively precise delivery rates. Such fluid delivery systems include various types of infusion pumps to administer medicinal fluids automatically and over extended periods of time. A typical infusion pump delivers the medicinal fluid into a patient's venous system utilizing a delivery channel, which usually includes the use of an administration tube (e.g., a polyvinyl chloride tube, etc.) connected to the patient utilizing some form of a catheter, needle, or the like.
For safety reasons and in order to achieve optimal results, it is desirable to administer the medicinal fluids such as, for example, intravenous (IV) fluids, intermittently and with a frequency as often as multiple times per day and in a controlled manner as prescribed by the physician. Depending on the frequency of administration, the patient is either repeatedly connected to and disconnected from an IV line or is continuously connected to an IV line between administrations. In either case, the intermittent medications are generally administered by trained personnel utilizing predefined procedures that often include a series of manual steps and a large number of disposable supplies. Each manual step in such procedures increases the risks associated with multiple manipulations and entry of IV sites.
Accordingly, it will be apparent that it would be desirable to provide a relatively low cost, low complexity system for the delivery of medicinal fluids. A closed-loop system in which a desired parameter is measured to control the system can provide the required accuracy. For example, in a closed-loop system, it would be preferable to measure flow with a sensor and to control an inexpensive fluid delivery pump based upon the measured flow rate so as to achieve a desired flow rate. The problem associated with such disposable deliverable systems for fluids, however, is that such a systems possesses too much compliance to accurately measure the dynamic flow at very low flow rates. Furthermore, the utilized sensor must be sterilized after use or disposed, which is very costly.
The majority of prior art systems utilize inferred flow measurements at the infusion pump. However, at low flow rates (e.g., ˜0.05 ml/hr) the time for the system to overcome the compliance in the disposable tubing (e.g., which can be ˜6-10 feet long) can be measured in hours, particularly in the case of a neo-natal patient where the catheter in the patient is an extremely small diameter tube and acts as a flow restrictor. While such systems reflect improvements in the art, they do not control fluid delivery in view of actual flow rates and the time required for the fluid to enter the patient increases. In some circumstances, therefore, such systems may require time ability to deliver fluids over a wide range of delivery rates including very low flow rates. Moreover, conventional manufacturing techniques tend to be expensive and, therefore, are not well suited for use in manufacturing disposable items.
Based on the foregoing, it is believed that a need exists for an improved differential force sensor for monitoring manual injections through the fluid line. A need also exists for an improved fluid delivery system for precisely controlling the flow of the fluid into the patient at very low flow rates and to minimize system compliance.